Manufacture of organolead compounds



a i ifi Patented Nov. 4, 1958 2,359,232 ,7 iMANUFACTURE-OFORGANOLEADCOMPOUNDS Sidney M. Blitzer and Tillmon H. Pearson, BatonjRouge, La., assignors to Ethyl Corporafion, New York, N. Y., :a corporation oFDelaware No Drawing. Application March 11,,1958

, serialrNmrzasriz- 4 v 6 Claims. (CL 260-437) a-number of years and, in general, is satisfactory. However, 'it has certain disadvantages which are overcome by practicing our invention. lt proceeds by reacting a sodiurmlead alloy, of composition controlled to correspond substantially to NaPb, with ethyl chloride according to "the following equation:

With the highest yields obtained thereby only about 22 percent of 'the' leadpresent in the NaPb alloy is converted to tetraethy'llead. "Under conditions of best operation of this process, 110- one heretofore, as far as We are aware,

has been able to' increase this yield of tetraethyllead by even a few percent, due to the'iriherent'limitation in yield as :is apparent from the consideration of the above 'equation. It should be noted that in this reaction at least 75 percent of the lead originally employed is not alkylated. 'Thus in this reaction, large quantities of lead must be recovered and reprocessed to NaPb alloy in order to make it economical. A further disadvantage of such a large quantityof unreacted lead is that valuable reaction space in the reaction vessel is occupied by materials which are essentially inert for the manufacture of tetraethyllead under present conditions and mode of operation.

Other processes for the production of organolead compounds, and in particular tetraethyllead, have been devised to consume the lead produced in the above equation. While such processes are satisfactory from the standpoint of lead consumption, they suffer an additional drawback in common with the present commercial process in that they require organo halide as the ethylating agent. One such process is that described in U. S. Patent 2,535,190 wherein lead as, for example, that produced in the commercial process, is treated with metallicimagnesium and ethyl chloride in the presence of 'a catalyst, preferablyan alkyl ether. Thus, in this process. aswell as the present commercial process, the tetraethyllead manufacturing operation is restricted by the necessary balance between the metallic sodium required and the organic chlorine in the ethyl chloride. 7

The classical Grignard synthesis for organolead compounds has been known for many years. Although proceeding readily, it has not been used commercially because of unfavorable'economics'. This process comprises reaction of an organomagnesium halide with a lead halide. Unfortunately, the lead halide is expensive and no known means for replacing it with an economical substitute has been shown heretofore.

It is therefore an object of this invention to provide a process for the manufacture of organo'lead compounds which overcomes the above objections'to the present corn- Inertial process and those processes which havebeen ment there over.

proposed earlier as well as more recently as an improve- Particularly, it is an object of the invention to increase the conversion of lead to tetraethy'llead above that obtained in present commercial practice Without requiring the use of metallic sodium, metallic lead, or alkyl'halogen compounds.

These and other objects .of this invention are accomplished by reacting-an inorganiclead chalkogen com- .pound with an organomagnesium halide. In accordance with this invention, .it has been discovered that to'produce organolead compounds itis unnecessary to start ,witha lead alloy,:a lead halide, or in .factto employ metallic lead at all. i

The process of'the present invention canbest be understood'by considering .the chemical equation involved. In general, the ;process.'proceeds(according to the equation 4RMgX+2PbY-' :PbR4+Pb+2MgX +2MgY where -R is an organic radical, X is a halogen of atomic weight greater :than '35, and Y is 3.,Cl1fllk0g8l1,"tht it is sulfur or oxygen. 'A satisfactory form of the lead .ito be employed in the process of this inventionis the common lead ore, galena, or leadsulfide. An additional satisfactory source ofilead for .the .present invention is lead oxide. Other lead oxides and sulfides can also be employed. In the preferred embodiment of this process the organic radicals are hydrocarbons and particularly arenon-aromatic or aromatic. Among the non-aromatic radicals we can employ alkyl or hydrocarbon. substituted alkyl radicals. vIn general, we prefer the lower alkyl radicals having up to about eight carbon atoms. Among the aromaticradicals which can be employed inthe above reaction are included'phenyl and hydrocarbon'substituted phenyl radicals such as the alkaryl radicals. 7 In general, aromatic radicals having up to 10 carbon atoms are satisfactory. Thus, thecompounds RMgXmay be considered alkylating or ary'lat'ing agents with're spect'to the .lead in the lead chalkogen compound represented by PbY.

Of greatest current importance from a. commercial standpoint is the'manufacture of 'tetraethyllead by the process of this invention. This embodiment can be illustrated by reference to the foliowingequation representing the preferred embodiment.

phenyl magnesium jbromide, diethylphenyl magnesium chloride and the like. In addition to thenormal alkyl 7 magnesium halidesindicated heretofore, the branched chainisomers can be employed Likewise, a mixture of Mom more compounds RMgX can be emplo-yed along With a le fi ti n c alys reprod en e po pounds containing a multiplicity of hydrocarbon radicals.

such as aluminum chloridgthe product comprises a mi r- "ture of tetramethyllead, trime'thylethyllead, dimethyldiethyllead, methyltriethylleaij'aird tetrae'thylleadfin an equilibrium propor tion.

By theprocessfof this invention, as much as S'Qfiercent of t'he le'ad inthe foregoing lead salts is directly converted a to oPg'aiioIead'rir i-n particular, inf-a c1611i1 a 1er ':i: ilfeiii bodiment, to tetra'ethyl lead'. A The rediainiiig portion-of the presence of ethyl chloride in the closed vessel.

lead is in a highly active form as lead metal and is ideally suited for employment in the commercial process employing sodium-lead alloy or in that which proposes the reaction of metallielead with an alkylating agent in the presence ofmagnesium'and a catalyst. Conversely,[the1lead so produced by this invention can be recycled economi- .eally to the present process by conversion to the appro- I-priatelead salt. r L l Our invention is adaptable to the produetion of organolead compounds generally, such as tetraethyllead, tetramethyllead, dimethyldiethyllead, tetraphenyllead, triethylphenyllead and tetrapropyllead. Nevertheless, .for convenience in describing our'invention hereafter, 'specifie reference will be, made to tetraethyllead, the most widely 1 known because'of its use as an antiknock agent. Whenever, in the following description, this material is referred V to, it is to be understood that other organolead compounds or mixtures can be made by our process.

1 Ge'nerally,'the" process of this invention is conducted as follows. Into a' reaction vessel, preferably a stirred autoclave, is placed the desired quantity of an inert liquid' carrier such as, for example, a hydrocarbon of medium boiling range. The appropriate lead salt, for

.example lead oxide in finely divided solid; form is introduced through a hopper containing a plugeock into the tion ensues and upon reaching the desired reaction tem-.

perature, cooling is provided through a jacket in the auto- I elave. In contrast to other processes for the manufacture of tetraethyllead, when thisinvention is employed it is not necessary to provide expensive and complex reflux equipment as, by proper choice of' the carrier liquid, the reaction can be conducted in a closed system. Thus, tetraethyllead can be produced without the co- This greatly facilitates control of the reaction and prevents the existence ofan otherwise hazardous operation. After completion of the reaction, the organolead compound produced is. in solution in the carrier liquid and the other products, namely the magnesium salt and metallie lead can be removed by filtration and the organolead compound removed from the carrier by distillation.

The operation described above can be varied and it is u not intended that this invention .be limited to this specific 7 sequence of addition. For example, the organo magnesium halide solution can be admitted to the. reactor f first'and then thefinely divided lead 'salt 'added.thereto y with agitation. In this instance the ether solution will A serve as the inert carrier or an additional inert carrier can be added. Other modifications .will be evident.

'Whilethe above operations were discussedin connection-with a batch operation, they can besuccessfully adapted to a eontinuous process. In addition to applying the aboveoperations to a continuous process, other modifications of a continuous process can be made, such las first mixing together all the reaction materials and :tion zone. r

It has been indicated that the process of the present invention is conducted in the presence of an inert carrier then passingthem continuously through a suitable reac-' ;liquid. .Hydrocarbons of appropriate boiling point with.

. respect to the organolead compound produced are satisfactory and can be chosen so as to provide a solution of the product suitable for other applications or so that they can be readily removed by distillation at a temperature atwhich'the organolead compound will not decompose.-

- Other inert earrier liquids are satisfactory and where the produet isa liquid such as, forexample, in the manufacture of tetraethyllead, the organolead compound itself can be employed as a carrier liquid. In such an operation, economies are effected by obviating the necessity of recovery by other means than merely filtration of the The ethers can also be employed as V Usually that'ether employed as diluent in the preparation of the organomagnesium halide :is f' used. Typical of this class of ethers is diethyl ether. In general, lower alkyl ethers having from one to six carbon co-produced solids. the inert carrier.

atoms in each alkyl group can be employed. Typiealof such ethers are dimethyl ether, methylethyl ethenadi butyl ether and dihexyl ether. .Another preferred class of solvents comprises the polyethers, such asthe dialkyl I ethers of glycols, including dimethyl ether of ethylene glycol, dimethyl ether of diethylene glycol, and the dialkyl ethers of the polyglycols, such as the dimethyl ether of." polyethylene glycol.

prises the liquid amines and liquid ammonia: The'principal criterion of choice therefore, ofa carrier, is the physicalcharacteristic of'the organolead compound produced, and the inertness of the liquid to the organo:

magnesium halide reactant. Certainof the aforementioned reactant carriers, while inert to thereactants, exhibit a beneficial effect on the reaction which may be considered catalytic in nature and contribute to the ease I ofreaction and rapidity of arriving at completion of the reaction at relatively lower temperatures and pressures.

In general, when conducting this process in the presence of a liquid carrier as above, the amount of carrier, should i be proportioned so as to provide adequaterheat removal facilities; Ingeneral, the load on the heat-.transfer 7 medium is proportional to the concentration or. relativev proportion. of the reactants and carrier. In a ,bateh op eration it is preferred to employ the liquid diluentin the proportion of as much as 1,000 parts per part of organometallic reactant. In a continuous operationi or in an operation providing the .maximum heatlh'ansfer medium, a more concentrated reaction mixture employed wherein as little as equal parts by weight: of if carrier and organometiallic reactant are employed. In

7 general, it has been found that a more concentratedreaction mixture-provides a rapid reaction and, provided. adequate heat removal means are provided this is an advantageas the organolead product is subjectedto, the if j elevated reaction temperature-for the shortest practieall' timethereby minimizing thermaldecompositionlor undesirable side reactions. 7 V The organomagnesium compounds employedin the process of this invention can be prepared'by methods i W well known in the art. For example, reaction' of thin magnesium turnings with an ethyl bromide in the presence of an ether produces ethyl magnesium bromide. 'Correspending reactions between magnesium and other halides of the desired organic group are employed for other embodiments of the present invention, ,It is not:,intended, however, that the scopeof this invention be limited to any particular methodof producing the hydroq carbon carrying reactant. j v

This invention can be further understood by the following detailed working example of one method ofprac ticing this invention as directed to the manufacture of tetraethyllead. V ple The reactor employed comprises an autoclave within-"i ternal'agitation, external heating means, and a means for cooling. Attached to the top thereof is provided a hopper for containing solid reactant having a plug coek which the solid reactant is admitted into the autoclave. The autoclave is flushed with dry nitrogen. To the autoclave is added 165 parts. of n-hexane. 'With agitation,

7.8 parts of lead oxide of particle size less than ,13 inch;

is admitted to the autoclave from the hopper. Thus-"a I suspension of the 'leadoxide. is formed. To this mixture A still further elass'of ether solvents comprises the cyclic ethers, such as dioxane and tetrahydrofuran. Another class of carrier liquids eom- V V is added a solution of 11.2 parts of ethyl magnesium bromide in 36 parts diethyl ether. The autoclave is then sealed. The resulting mixture is heated to about 114 C. Since the reaction is exothermic, the heat is then removed and the mixture is cooled to maintain a temperature between about 114 to 122 C. When the temperature drops, as the reaction proceeds, heat is again applied to maintain the temperature within the aforementioned range. At the end of 3 hours the agitation is stopped. The mixture is cooled to room temperature and the pressure in the system is released. It is then filtered to remove solids. The filtrate is washed with an equal volume of water and the organic layer transferred to a still for the removal by vacuum distillation of the ether and n-hexane and recovery of the tetraethyllead from the mixture. The conversion obtained was 13 percent.

Similarly, when methyl magnesium bromide, propyl magnesium chloride, phenyl magnesium iodide, benzyl magnesium bromide, ethyl magnesium iodide, and butyl magnesium chloride are employed in the process of the foregoing example, satisfactory yields of tetramethyllead, tetrapropyllead, tetraphenyllead, tetrabenzyl lead, tetraethyllead, and tetrabutyllead are produced, respectively.

In general, the reaction of this process is completed within a relatively short period at elevated temperatures, but a somewhat longer time is required at lower .temperatures. In general, a reaction time of between about one-half to twenty hours is employed. In particular, in the manufacture of tetraethyllead with ethyl magnesium bromide and lead sulfide or oxide, we prefer to employ a reaction time of about ten hours or less.

The pressure employed in the reaction vessel is not critical and is usually the autogenous pressure created by the carrier liquid at the temperature employed. Since organolead compounds are relatively toxic, it is desirable to employ a closed vessel in conducting this reaction which may create an elevated pressure if low boiling carrier liquids are employed.

The temperature required to initiate the self-sustaining reaction of this invention varies with the organolead compound being produced. In general, with the lower alkyl lead compounds such as tetraethyllead, it is preferred to employ temperatures in the range of 25 F to 150 C. With aryllead compounds, for example tetraphenyllead, it is preferred to operate in the range of 50 to 150 C.

As the lead chalkogen reactants in this invention are solids, and generally a solvent therefore is not employed, it is preferred in order to provide a relatively rapid and controllable reaction to employ these reactants in finely divided form, or at least in the form of small granules.

While it was indicated above that in general a catalyst is not required for the practice of this invention, certain materials do exhibit a catalytic eflect upon the reaction and, in many instances, their inclusion in the reaction provides a smoother operation. Typical of such mate rials are heavy metal iodides as well as iodine itself, organic iodides, certain ketones such as acetone and methyl ethyl ketone, and ethers and amines as indicated heretofore.

The following detailed examples serve to illustrate additional specific embodiments of the present invention. However, the invention is not intended to be limited thereto.

Example II The procedure of Example I is followed essentially as described with the exception that the reaction temperature is maintained between 114 and 118 C. for 3% hours. In this instance, 11.2 parts of ethyl magnesium bromide in 36 parts diethyl ether are reacted with 5.98 parts of finely divided lead sulfide in 165 parts of henzene. Tetraethyllead is obtained in high yield.

In place of the benzene employed in the foregoing example as an inert carrier liquid, equally good results are obtained when toluene, xylene, triethyl amine, or diphenyl are employed. In addition to the ingredients specified in the foregoing example, thermal stabilizers may be employed, such as for example naphthalene and styrene to permit operation of the reaction at still higher temperatures without concomitant decomposition of the tetraethyllead so produced.

Example 111 The autoclave of Example I is modified to include a reflux condenser. During the operation, an atmosphere of dry nitrogen is maintained in the reactor. Lead oxide is reacted with amyl magnesium chloride in essentially stoichiometric amounts in a C -C hydrocarbon petroleum fraction at the reflux temperature for four hours thus permitting operation at atmospheric pressure. Tetraamyllead is recovered in high yield.

Similarly, when amyl magnesium bromide is reacted with lead sulfide as in the foregoing example, and at a temperature between about to 0, equally satisfactory results are obtained.

Example IV When reacting finely divided lead oxide with phenyl magnesium bromide in essentially stoichiometric amounts in cyclohexane at the reflux temperature for five hours, tetraphenyllead is obtained.

Example V The procedure of Example III is repeated reacting finely divided lead oxide with benzyl magnesium bromide in excess of 0.1% of the theoretical. The reaction is conducted in di-n-butyl ether at the reflux temperature for sixteen hours. Tetrabenzyllead is obtained in high yield.

The following example demonstrates one embodiment of this invention wherein tetraethyllead is employed as a carrier..

Example VI A similar solution of ethyl magnesium bromide as em-,

ployed in Example I is prepared and 30 parts of tetra ethyllead are added thereto. This mixture is subjected to distillation under vacuum wherein a substantial proportion of the diethyl ether'is vaporized from the mixture to result in a mixture of ethyl magnesium bromide in tetraethyllead. The autoclave is charged with parts of tetraethyllead and the finely divided lead oxide is added thereto. followed as described. Upon completion of the reaction and separation, tetraethyllead is recovered in high yield.

We claim:

1. A process for making hydrocarbon lead compounds which comprises reacting a hydrocarbon magnesium halide wherein the hydrocarbon radical has up to about 10 carbon atoms with a lead chalkogen wherein the chalkogen is selected from the group consisting of oxygen and sulfur.

2. A process for making alkyl lead compounds which comprises reacting an alkyl magnesium halide wherein the alkyl group contains less than about 8 carbon atoms with a lead chalkogen wherein the chalkogen is selected from the group consisting of oxygen and sulfur.

3. The process of-claim 2 wherein the reaction is conducted at a temperature between about 25 to 150 C. in the presence of an essentially inert carrier'liquid.

4. The process for the manufacture of tetraethyllead which' comprises reacting ethyl magnesium bromide with l f lead oxide.

5. The process of claim 4 wherein the reaction is con- No references cited.

The procedure of Example I is then 

1. A PROCESS FOR MAKING HYDROCARBON LEAD COMPOUNDS WHICH COMPRISES REACTING A HYDROCARBON MAGNESIUM HALIDE WHEREIN THE HYDROCARBON RADICAL HAS UP TO ABOUT 10 CARBON ATOMS WITH A LEAD CHALKOGEN WHEREIN THE CHALKOGEN IS SELECTED FROM THE GROUP CONSISTING OF OXYGEN AND SULFUR. 